Coating machine having a timer for continuously forming a coating of uniform thickness on a substrate

ABSTRACT

A coating apparatus which comprises a feeding means to feed a coating liquid, a coating liquid applicator having a slot extending in one direction to discharge the coating liquid fed by the feeding means, and a conveying means to move at least either the coating liquid applicator or a substrate to be coated with the coating liquid relatively one to the other, comprising: (a) a first control means which comprises (a-1) a position detecting means to detect positions of the coating liquid applicator or the substrate which is moved by the conveying means, and (a-2) a controller capable of stopping the coating liquid applicator or the substrate which is moved by the conveying means at a position detected by the position detecting means such that a start-of-coating line of the substrate is in register with the slot of the coating liquid applicator and capable of starting the movement of the coating liquid applicator or the substrate which is stopped at the position; and (b) a second control means which comprises a timer controller capable of transmitting a signal to the controller of the first control means for the movement of the coating liquid applicator or the substrate which is stopped at the position after a desired period which begins with commencement of feeding the coating liquid and is needed for forming a coating liquid bead which is in contact with both the exit aperture of the slot of the coating liquid applicator and the substrate at the start-of-coating line.

The instant application is a national stage application ofPCT/JP95/02741, filed Dec. 27, 1995.

TECHNICAL FIELD

The present invention relates to a coating method and coating apparatusfor the application of coating liquids, particularly to a coating methodand coating apparatus to produce stably a coating on a flat surface of asheet substrate, which are suitable for application in electronicindustrial areas such as semiconductor production. The invention alsorelates to a color filter manufacturing method based on said coatingmethod, color filters thus manufactured, and a method for manufacturingcoated sheet products such as color filters for liquid crystal displaysand solid-state camera tubes, optical filters, printed circuit boards,integrated circuits and other semiconductor devices.

BACKGROUND ART

In recent years, the production of coatings through thin and uniformapplication of various coating liquids has been strongly demanded toform coatings over plastics substrates for optical filters, glasssubstrates for liquid crystal displays, and glass substrates for colorfilters, etc. and to form photoresists or protective layers on printedcircuit boards or wafers, etc. in an integrated circuit or semiconductormanufacturing process. This requires the industrial-scale production ofcoatings on small-size substrates, in many cases less than 1 meter longin the coating direction, and necessitates the adoption of a sheetcoating method which involves the feeding of substrates to the coater,one by one, application of coating liquids, and transfer of the coatedsubstrates to the next process such as drying.

The methods which have been used conventionally and widely for suchcoating include the use of a spin coater, bar coater and roll coater.

Of these, the spin coater method which is widely used to formphotoresist over a semiconductor wafer can apply coatings on a spinningsubstrate to be coated by dropping a droplet of coating liquid at thecenter of the substrate and spreading it over the surface by means of acentrifugal force. This method can produce uniform coatings over theentire surface of a substrate to be coated with a high thicknessaccuracy by choosing coating liquids suitable for this method. With themethod, however, only several to ten percent of the coating liquiddropped on the surface of the substrate can be utilized for the actualformation of a coating, and the remainder, more than 90%, of that isremoved from the surface and thrown away. Thus, a very large amount ofcoating liquid is required to obtain a film with a predeterminedthickness, making the method uneconomical. In some cases, moreover, thecoating liquid is deposited on an edge or the bottom surface of thesubstrate, or waste coating liquid scattered within the equipment gelsor solidifies, which reduces stability and cleanliness, leading todegradation in the quality of the coated product.

The roll coater method involves the transfer of a coating liquid ontothe surface of a substrate to be coated via a rubber roll, and iscapable of applying a coating on a long material or on a continuousmaterial wound onto a reel. However, since the coating liquid issupplied from a pan to an application roll and then to the substrate,exposure to the air becomes prolonged, which gives rise to vulnerabilityto degradation due to moisture absorption and oxidation, as well as theintrusion of foreign matter. As a result, degradation in the quality ofthe coated product tends to occur.

The bar coater method involves the application of a coating liquid ontoa substrate to be coated using a bar made of a rod on which thin wire iswound. The problem with this method is that line marks are easily formedon the coating due to the contact between the wire wound on the rod andthe coated substrate.

The die coater method, on the other hand, has been used conventionallyand widely in areas where the production of thick coatings or continuousapplication of high-viscosity coating liquids is required. In case thata coating is formed on a substrate to be coated by using a die coater,the coating liquid is supplied through a slot of the die of the diecoater to produce a pool of the coating liquid, called a coating liquidbead, between the die and the substrate which is moving relatively tothe die running while maintaining a constant gap between them, and thecoating liquid is pulled out as the substrate runs to form a coating, ashas been disclosed, for example, in U.S. Pat. No. 3,526,535. Continuousproduction of a coating is possible by supplying the same amount ofcoating liquid as that consumed in the coating formation.

Thus, a coating produced with a die coater can achieve a uniformthickness with a considerable degree of accuracy. There is hardly anywaste of coating liquid, and as the coating liquid supply path to theslot outlets is enclosed, the degradation of the coating liquid andintrusion of foreign matter can be prevented, thus enabling the methodto enhance the quality of the resultant coating. This method also makesit possible to provide a rectangular-shaped coating at any desiredposition of a substrate to be coated.

In light of these problems associated with the spin coater, bar coateror roll coater method, a proposal to use the die coater method for themanufacture of color filters has been made recently in Japanese PatentPublication Laid-Open (Kokai) Nos. 5-11105 (1993) and 5-142407 (1993).

However, these die coaters lack a substantial history in theirapplication to sheet substrates and are not sufficiently high in thelevels of coating position accuracy, film thickness accuracy,reproducibility, stability, etc., which are essential for the continuousmass production of high quality coated products.

There seem to be four major technical reasons for this.

Firstly, adequate consideration has not been given to the formation anddisappearance of a coating liquid bead, despite their importance forstable coating operations.

Namely, when a die coater is used to form a coating on substrate fed ina sheet-form, the application of the coating liquid inevitably becomesintermittent, so that disturbance of a coating liquid bead ordisappearance of a coating liquid bead occurs at the start-of-coatingline and/or the end-of-coating line on the substrate, regardless ofwhether the coating liquid is discharged continuously or intermittently.This makes it difficult to maintain a stable and suitable coating liquidbead over the entire coating area, and a uniform coating cannot beachieved until the bead reaches a stable state. If the stabilization ofthe bead requires a long time, it will lead to an increase in the areawhere the coating thickness is uneven, and the portion of the substratewhich can be used effectively becomes extremely small. Regarding theformation and disappearance of a coating liquid bead, a method ofproducing a connecting bead, i.e. coating liquid bead, by generatingpulses in supplying coating liquid has been disclosed in U.S. Pat. No.4,938,994. However, by this method, the start-of-coating line cannot beaccurately fixed since the substrate is moving while a coating liquidbead is formed and stabilized, and the length of the coated portion ofthe substrate before a coating liquid bead has been stably formedincreases, thereby decreasing the portion of the substrate over whichthe required film thickness is obtained uniformly.

Secondly, no consideration is given to the relative positions of thesubstrate and the slot of the die. Where shifts occur to their relativepositions or their reproducibility is poor, the position of the coatedarea may also shift, possibly with large fluctuations well beyond theallowable range. This is particularly crucial when a rectangular coatingis to be formed on an inside portion of the surface of the substrate.

Thirdly, adequate consideration is not given to achieving a uniformclearance, i.e. the distance between the substrate and the exit face ofthe slot of the die, which has a major impact on the maintenance of acoating liquid bead.

Namely, when producing a coating with a uniform thickness on a substrateto be coated by using a die coater, the clearance must be kept constantover the entire width of the die of the die coater. The conventional wayof keeping the distance from the substrate constant over the entirewidth of the die of the die coater is to measure the parallelism betweenthe die and the substrate with a gauge etc. while the die is mounted onits support, and, if the parallelism between them is not satisfactory,manual adjustments to the condition of the die mounted on the supportare made. Dies need to be washed regularly, since their continuous usegradually renders their interior dirty. However, if the adjustment worknecessary after the mounting of the washed die onto the die coater isundertaken manually, it becomes cumbersome and requires a considerableamount of time to complete, which reduces the productivity. With manualadjustment, the accuracy of clearance depends on the workmanship ofindividual workers, making it impossible to always achieve a requiredaccuracy with high reproducibility. In particular, when a thin coatingis to be formed, a minute deviation in parallelism created through theadjustment process results in a large fluctuation in the thickness ofthe coating produced, greatly reducing the quality of the coating.

Moreover, the substrate itself fluctuates in thickness, and in addition,the vertical movement of the table carrying the substrate causesfluctuations in the clearance as the substrate travels. Depending on theseverity, this can constitute an obstruction to improving the accuracyof coating thickness.

Usually, the linear slider which guides the table is provided by alinear motion guide. A linear motion guide here refers to a mechanism inwhich numerous balls are provided in such a way that not only can eachof them rotate on its axis but they can also circulate along apredetermined path (hereinafter referred to as a revolution), so thatthe table can be moved smoothly as a result of the rotation andrevolution of these balls.

However, when a table with a linear slider composed of a linear motionguide is used, the vertical movement of the table cannot be reduced to alow level because it undergoes considerable pitching and yawing. As aresult, fluctuations in the clearance become large, making it impossibleto control the coating thickness with high accuracy, i.e. to apply auniform coating over the entire surface of the substrate.

A likely solution to this is the use of roller bearings in place of alinear motion guide to improve the traveling accuracy of the table, i.e.to reduce its vertical movement. However, as the traveling speed of thetable increases up to a certain high-speed region, slipping starts tooccur between the table support and roller bearings, which causeseventually the table supports to run off from the rollers, and a problemin that it is incapable of prolonged use under high-speed conditions.

Fourthly, there have been problems associated with the drying and heatcuring of the coating liquid in the manufacturing of coated sheetproducts such as color filters, as described below.

Conventional methods of manufacturing coated sheet products such ascolor filters usually include drying and heat curing, by the oven methodin which a coating liquid is applied over a glass substrate using a spincoater and then heated with the coated glass substrate held in a heatedatmosphere, and by the hot plate method in which the coated glasssubstrate is placed on a hot plate. Coating by means of a spin coatertakes some 60 seconds, and in addition, a considerable amount of thesolvent in the coating liquid evaporates to accelerate the drying whilethe excess coating liquid is dissipated. This increases theconcentration and viscosity of the coating liquid, resulting in a lowfluidity at the end of the coating process. Therefore, the use of theoven or hot plate method to dry and heat-cure coatings rarely results inthe spoiling of the coated surface due to external disturbances such aschanges in the evaporation pattern, uneven temperature distribution andconvection.

However, if a die coater and a spin coater are used to apply the samecoating liquid on a glass substrate, the die coater is much shorter inthe coating time compared with the spin coater, and in the absence ofany particular factors which contribute to accelerated evaporation, thesolvent does not evaporate much before the end of the coating process,so that the concentration, viscosity and liquidity of the coating liquidremain almost unchanged. Therefore, the use of the same drying andheat-curing method as in the case of a spin coater has so far resultedin coating defects. Namely, when the coating liquid is heat-cured usingthe hot plate method, marks of several pins used to support the glasssubstrate, marks of the arm used to convey the substrate and marks ofthe hot plate notches provided for the conveyance tend to be leftundesirably on the coating. This problem occurs as the pins, arm andnotches come into contact with the glass substrate, and this causes anuneven temperature distribution due to localized increases or decreasesin the temperature of the affected parts of the glass substrate,resulting in a variation in the evaporation speed of the coating liquidsolvent over the substrate surface. With the oven method, too, surfaceturbulence marks and other defects due to convection sometimes occur, ifthe heating temperature is raised too high in an attempt to increase thedrying speed. Also, both methods may cause surface defects such asglossy spots, as the history of the evaporation process of the solventremains on the surface of the coating.

Moreover, there is no known method suitable for manufacturing a coatedproduct which comprises a rectangular coating formed on an inner portionof a surface of a sheet substrate. The simple utilization of aconventional method is fraught with problems such as surfaceimperfections, and in severe cases, the edge of such a rectangularcoating on a substrate cannot be kept straight as a result of thecoating liquid flowing out from a part of the edge of the rectangularregion.

DISCLOSURE OF THE INVENTION

The present invention was made in light of the above problems, and itsmain object is to provide a coating method and coating apparatus whichare capable of producing stably a uniform coating over a suppliedsubstrate with good reproducibility and without compromising theadvantages of a die coater, such as economy, high precision thin-filmcoating, and containing the coating liquid all the way. In particular,the invention is intended to provide a coating method and coatingapparatus which can be favorably applied to sheet substrates, and toprovide a method for manufacturing coated sheet products.

In more specific terms, the objects of the invention are as listedbelow:

First, a coating liquid bead necessary for a stable coating operation isto be formed at an early stage at the beginning of the coating process.

Second, accuracy in the relative positions of the die slot and thesubstrate is to be improved.

Third, the accuracy of the clearance in the width direction is to beimproved to achieve a dramatic reduction of fluctuation in coatingthickness in the direction of the width of the coating liquiddischarger.

Fourth, fluctuation of the clearance in the traveling direction is to bereduced by introducing a linear slider provided with roller bearingswhich permit stable and smooth bi-directional traveling over a prolongedperiod without too much sacrifice of traveling speed and which candramatically reduce vertical movements compared with the use of a linearmotion guide.

Fifth, a method and apparatus for manufacturing coated sheet productssuch as color filters are to be provided by which high quality coatedproducts, especially those high quality coated products with arectangular-shaped coating portion formed on the inside surface of thesubstrate, can be produced without generating defects during the curingof the coating liquid applied over the substrate.

An embodiment of the coating method according to the present inventionis a coating method, wherein a coating liquid feeder supplies a coatingliquid to a coating liquid applicator having a coating liquid dischargeslot, with at least either the coating liquid applicator or a substrateto be coated being moved relatively one to the other to form a coatingwith a predetermined thickness on the substrate, comprising the stepsof: keeping at rest the substrate at a position where a start-of-coatingline of the substrate is in register with the coating liquid dischargeslot of the coating liquid applicator; commencing the discharge of thecoating liquid through the coating liquid discharge slot; forming acoating liquid bead which is in contact with both an exit aperture ofthe coating liquid discharge slot and the start-of-coating line of thesubstrate; and subsequently commencing movement of at least either thecoating liquid applicator or the substrate relatively one to the other.

A coating method of this embodiment makes it possible to accuratelydetermine the start-of-coating line and produce a high accuracy coating,because by this method, after discharge of the coating liquid startswhile the substrate to be coated is still at rest in register with thecoating liquid discharge slot and the formation of the coating liquidbead is assured, the substrate is moved relatively to the coating liquiddescharge slot while rendering the coating liquid bead stable.

Another embodiment of the coating method according to the presentinvention is a coating method wherein a coating liquid feeder supplies acoating liquid to a coating liquid applicator having a coating liquiddischarge slot while a substrate to be coated is held and conveyed by acarrier to form a coating on the substrate, comprising the steps of:conveying the substrate by driving the carrier; stopping the substrateso that a start-of-coating line of the substrate lies below the coatingliquid applicator; activating the coating liquid feeder to commencedischarge of the coating liquid from the coating liquid discharge slot;forming a coating liquid bead over at an exit aperture of the coatingliquid applicator throughout the slot in a widthwise direction; andsubsequently commencing movement of the substrate using the carrier.

A coating method of this embodiment makes it possible to produce ahighly accurate coating from the start-of-coating line, compared withother methods wherein the substrate starts moving before the completionof the formation of a coating liquid bead, because by this methoddischare of the coating liquid through the coating liquid discharge slotis started by activating the coating liquid feeder after stopping thesubstrate so that the start-of-coating line of the substrate lies belowthe coating liquid applicator such as a die, and also because theconveying of the substrate using the carrier such as a table or a stageis started after forming a coating liquid bead over at the exit apertureof the coating liquid applicator throughout the slot in a widthwisedirection. This makes it possible to increase the ratio of the length ofthe area over which the coating thickness is almost uniform to that ofthe overall coated area.

In an embodiment of the color filter manufacturing method according tothe present invention, color filters are manufactured using a coatingmethod as represented by one of the above embodiments.

A color filter manufacturing method of this embodiment makes it possibleto supply extremely high quality color filters with high efficiency, ashigh accuracy coated products can be obtained without wasting thecoating liquid.

In another embodiment of the color filter manufacturing method accordingto the present invention, color filters are produced by using a coatingmethod as represented in one of the above embodiments to apply at leastone of the following layers: protective layer, pigmented layer,photo-shielding resin layer and photoresist layer.

A color filter manufacturing method of this embodiment makes it possibleto supply extremely high quality color filters having at least one ofthe following: protective layer with a low in-plane thicknessfluctuation, pigmented layer or phto-shielding resin layer with a lowin-plane fluctuation in spectral characteristics, and photoresist layerwith a uniform coating thickness and a low dimensional fluctuation whichpermits high accuracy processing of pixels.

Yet another embodiment of the color filter according to the presentinvention is a color filter which is obtained by using either of thepreceding color filter manufacturing methods.

A color filter of this embodiment can be an extremely high quality colorfilter which can have a pigmented layer and/or photo-shielding resinlayer with a low in-plane fluctuation in chromaticity, a protectivelayer with a low in-plane thickness fluctuation, etc.

An embodiment of the coated sheet product manufacturing method accordingto the present invention is a coated sheet product manufacturing methodcomprising: (A) a step wherein at least either a coating liquidapplicator having a coating liquid discharge slot or a sheet substrateto be coated is moved relatively one to the other, followed by keepingat rest the sheet substrate so that a start-of-coating line of the sheetsubstrate is maintained in register with the coating liquid dischargeslot; (B) a step wherein a coating liquid is supplied from a coatingliquid feeder to the slot of the coating liquid applicator, followed bycommencing discharge of the coating liquid through the discharge slot;(C) a step wherein a coating liquid bead which is in contact with boththe exit aperture of the slot of the coating liquid applicator and thestart-of-coating line of the sheet substrate is formed, followed bycommencing movement of at least either the coating liquid applicator orthe sheet substrate relatively one to the other so that a coating with apredetermined thickness is formed on the sheet substrate; (D) a stepwherein the coated sheet substrate with the coating is carried into avacuum dryer; and (E) a step wherein the coated sheet substrate is driedunder a pressure of 20 Torr or less and at a temperature in a range of30° C.-180° C.

By a coated sheet product manufacturing method of this embodiment, asheet substrate on which has a relatively large amount of solvent afterthe coating operation by a coating liquid discharger such as a diecoater is dried under vacuum and at a relatively low temperature, andtherefore the decrease in the viscosity of the coating liquid at theearly stage of the drying process is minimized, which permits theprevention of the migration of the coating liquid due to externaldisturbances and warping of the coated substrate due to thermal strain,making it possible to cure the coating without sacrificing the highcoating accuracy and smooth coating surface achieved during the coatingprocess.

An embodiment of the coating apparatus according to the presentinvention is a coating apparatus which comprises a feeding means to feeda coating liquid, a coating liquid applicator having a slot extending inone direction to discharge the coating liquid fed by the feeding means,and a conveying means to move at least either the coating liquidapplicator or a substrate to be coated relatively one to the other,comprising: a first control means by which a start-of-coating line ofthe substrate is kept at a position in register with the coating liquidapplicator slot; and a second control means by which movement of atleast either the coating liquid applicator or the substrate to be coatedis commenced to move one relatively to the other after forming a coatingliquid bead which is in contact with both the exit aperture of the slotof the coating liquid applicator and the start-of-coating line of thesubstrate.

By a coating apparatus of this embodiment, the substrate to be coatedcan be kept at rest at the predetermined position and the coatingoperation can be started after the formation of a coating liquid bead,making it possible to accurately fix the position of thestart-of-coating line, produce a coating with high thickness accuracy,and achieve a constant thickness immediately after the start of thecoating operation so that the useful coated area of the substrate can beincreased.

Another embodiment of the coating apparatus according to the presentinvention is a coating apparatus which comprises a feeding means to feeda coating liquid, a coating liquid applicator having a slot extending inone direction to discharge the coating liquid fed by the feeding means,and a conveying means to move at least either the coating liquidapplicator or a substrate to be coated relatively one to the other,comprising: a positioning means which determines a position of thesubstrate, before bringing the coating liquid applicator and thesubstrate close to each other.

By a coating apparatus of this embodiment, the substrate to be coatedcan be positioned on the carrier within a predetermined accuracy limit,and this eliminates misalignment in the width direction between thecoating liquid discharger, such as a die, and the coated area on thesubstrate and also eliminates shift in the start-of-coating line,allowing a coating to be produced accurately within a predeterminedcoating area. A significant shift in the position of the coating areacould lead to a great fluctuation in the coating thickness at thebeginning and/or the end of the coating area, but this does not happenwith this embodiment of the coating apparatus since positioning iscarried out accurately, and a uniform coating thickness can be achievedthroughout the coating area with little fluctuation and greatreproducibility after repeated coating operations.

A still another embodiment of the coating apparatus according to thepresent invention is a coating apparatus which comprises a feeding meansto feed a coating liquid, a coating liquid applicator having a slotextending in one direction to discharge the coating liquid fed by thefeeding means, and a conveying means to move at least either the coatingliquid applicator or a substrate to be coated relatively one to theother, comprising: a gap measurement means by which gaps between thebottom surface of the discharge outlet of the coating liquid applicatorand the top surface of the carrier for conveying the substrate aremeasured at two predetermined positions spaced from each other prior tothe commencement of the coating operation for the substrate, and acoating liquid applicator driving means which rotates the coating liquidapplicator so that the two gaps become equal to each other.

By a coating apparatus of this embodiment, the thickness of the coatingproduced on the surface of the substrate to be coated can be madeuniform over the entire width, because the parallelism between thebottom surface of the coating liquid discharger, such as a die, and thetop surface of the carrier, such as a table, is first adjusted byrotating the coating liquid discharger to make the two gaps equal toeach other prior to the beginning of the coating operation for thesubstrate, with a coating being produced subsequently on the surface ofthe substrate by allowing the carrier to move the substrate whiledischarging the coating liquid from the coating liquid discharger. Theadjustment of the two gap readings between the coating liquid dischargerand the carrier, i.e. the adjustment of their parallelism, can becarried out with high reproducibility and high accuracy, since it doesnot rely on human skills. The adjustment of parallelism can be carriedout using a method other than the rotation of the coating liquiddischarger, as long as it is capable of moving each end of the coatingliquid discharger individually.

Another embodiment of the coating apparatus according to the presentinvention is a coating apparatus which produces a coating on a surfaceof a substrate by discharging a coating liquid from a coating liquidapplicator while moving the substrate by means of a table which carriesthe substrate, comprising: the table supported by roller bearings on abase so as to travel back and forth freely along a predetermineddirection while a driving force is transmitted via a ball screwmechanism, and a stopper to block forcibly the movement of the rollerbearings, which is provided at a predetermined location near the limitof the roller bearings movement caused by a bi-directional travel of thetable.

By a coating apparatus of this embodiment, if the table carrying thesubstrate to be coated reaches a high traveling speed which leads tocause slip between the table and the roller bearing, the possibility ofthe roller bearing moving to its movement limit in either direction dueto a difference between the table's forward and backward travelingspeeds can be eliminated, because a roller bearing stopper to block themovement of the roller bearing is provided at a predetermined locationnear the limit of the roller bearing movement which accompanies thebi-directional travel of the table. This makes it possible to maintain ahigh traveling speed for the table, and allows long term stable andsmooth bi-directional movement. As a result, it becomes possible tointroduce a roller bearing which allows the clearance between the bottomsurface of the coating liquid discharger and the top surface of thesubstrate to be maintained with high accuracy as the substrate travelsalong. It is preferable that the roller bearing stopper has a shockabsorbing substrate to block the movement of the roller bearing softly,which serves to extend the life of the roller bearing by mitigatingdamage.

Another embodiment of the coating apparatus according to the presentinvention is a coating apparatus which produces a coating on a surfaceof a substrate by discharging a coating liquid from a coating liquidapplicator while moving the substrate by means of a table which carriesthe substrate, comprising: the table supported by roller bearings on abase so as to travel back and forth freely along a predetermineddirection while a driving force is transmitted via a ball screwmechanism, a table lifter provided so as to lift up the table when thetable has repeated its back-and-forth movement a predetermined number oftimes, and a roller bearing backward mover provided so as to move theroller bearings backwards following a lift of the table by the tablelifter.

By a coating apparatus of this embodiment, the possibility that anexcessively increased speed of the table carrying the substrate to becoated may cause slip between the table support and the roller bearingto allow the table to reach its movement limit to hamper the function ofthe roller bearing can be eliminated by moving the roller bearingbackwards before the roller bearing reaches its movement limit. Thisalso makes it possible to introduce a roller bearing which contributesto the improvement of the accuracy of the clearance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram of a die coater including the coatingliquid supply system.

FIG. 2 shows an isometric projection of a die coater embodiment.

FIG. 3 shows a sectional view of a die used in a die coater embodiment.

FIG. 4 shows a time chart of the operation of each device used in a diecoater embodiment.

FIG. 5a shows a schematic diagram of a wiping equipment.

FIG. 5b shows an enlarged X--X sectional view of the wiping equipmentshown in FIG. 5a.

FIG. 6 shows an isometric projection of another die coater embodiment.

FIG. 7 shows a plan view of a positioning device embodiment.

FIG. 8 shows a plan view of another positioning device embodiment.

FIG. 9 shows an isometric projection of a still another positioningdevice embodiment.

FIG. 10 shows a thickness profile of a coating in the travelingdirection in a case where the positioning has been performed.

FIG. 11 shows a thickness profile of a coating in the travelingdirection in a case where the positioning has not been performed.

FIG. 12 shows a thickness profile of a coating in the width direction ina case where the positioning has been performed.

FIG. 13 shows a thickness profile of a coating in the width direction ina case where the positioning has not been performed.

FIG. 14 shows a flowchart of the parallelism adjustment process.

FIG. 15 shows a detailed enlarged sectional view of the linear slider.

FIG. 16 shows a diagram of the configuration of the portion for blockingthe movement of the roller bearing.

FIG. 17 shows a diagram of the configuration of the portion for liftingthe table.

FIG. 18 shows a diagram of the configuration of the portion for movingthe roller bearing backwards.

FIG. 19 shows a flowchart of the roller bearing's backward movementprocess carried out by the devices given in FIGS. 17 and 18.

FIG. 20 shows a diagram of an embodiment of the coated sheet productmanufacturing method.

FIG. 21 shows a typical thickness profile of a coating obtained inExample 1.

FIG. 22 shows a simplified plan view of the appearance of a typicalcoating obtained in Example 1.

FIG. 23 shows a typical thickness profile of a coating obtained inComparative Example 1.

FIG. 24 shows a simplified plan view of the appearance of a typicalcoating obtained in Comparative Example 1.

FIG. 25 shows a schematic diagram of the operation of each device inComparative Example 2.

FIG. 26 shows a typical thickness profile of a coating obtained inComparative Example 2.

FIG. 27 shows a simplified plan view of the appearance of a typicalcoating obtained in Comparative Example 2.

Symbols shown on the drawings stand for the following:

BEST MODE FOR CARRYING OUT THE INVENTION

The best mode for carrying out the invention is described below withreference to the drawings.

FIG. 1 shows an overall configuration of an apparatus for performing acoating method according to the present invention.

This coating apparatus for a sheet substrate has a coating liquid tank50; a syringe pump 44; a die 40 which is the coating liquid dischargerprovided with a coating liquid discharge slot 64; a table 6 which ismoved in back-and-forth directions by a driving mechanism comprising afeed screw 14 and a threaded nut-like connector 16; a position sensor 57comprising an optical sensor which detects the position of a glasssubstrate A, i.e. the substrate to be coated, placed on the table 6; asequencer 56 which controls the output signal from the position sensor57 and, AC servomotor 18 which powers the feed screw 14; and a computer54 which controls the sequencer 56 and the syringe pump 44.

A coating liquid delivery hose 42 stretches from the die 40, and the endof the delivery hose 42 is connected to the delivery port of anelectromagnetic changeover valve 46 for the syringe pump 44. A suctionhose 48 runs from the suction port of the electromagnetic changeovervalve 46, and the end of this suction hose 48 is connected to a coatingliquid feed tank 50.

The pump proper 52 of the syringe pump 44 is selectively connectable toeither the delivery hose 42 or suction hose 48 via the changeover actionof the electromagnetic changeover valve 46. The electromagneticchangeover valve 46 and the pump proper 52 are electrically connected tothe computer 54, and their operation is controlled by control signalsfrom the computer 54. The lifting actuator 21 and thickness sensor 22are also electrically connected to the computer 54. The syringe pumpused here is a piston-type constant volume dischargeable pump, but apositive displacement pump such as a gear pump or a diaphragm pump mayalso be used as a constant volume dischargeable pump for this invention.The syringe pump comprises of a piston and a cylinder, and the preferredsubstrates for them include stainless steel and other metals, glass(like in a syringe), and ceramics, while plastics and polymer resinssuch as Teflon may also be used depending on the type of the coatingliquid. It is also possible to limit the use of plastics and polymerresins such as Teflon to parts of the piston which come into contactwith the coating liquid.

To control the operation of the syringe pump 44, a sequencer 56 is alsoconnected to the computer 54. The sequencer 56 performs the sequentialcontrol of the AC servomotor 18 for the feed screw 14 on the side of thetable 6 and the AC servomotor 30 (not shown on the drawing) for thelifting mechanism 26 (FIG. 2). For this sequential control, thesequencer 56 receives signal inputs such as those indicating theoperational status of the AC servomotors 18 and 30, those from theposition sensor 57 which detects the position of the table 6, and thosefrom a sensor (not shown on the drawing) which detects the operationalstatus of the die 40. From the sequencer 56, signals indicating theirsequential operation are then sent to the computer 54.

Instead of using a position sensor 57, it is also possible toincorporate an encoder into the AC servomotor 18 and allow the sequencer56 to detect the position of the table 6 based on the pulse signaloutputted by the encoder.

Although not shown on the drawing, the die coater is equipped with aloader to load the table 6 with a glass sheet A for a color filter assheet substrate to be coated and an unloader to remove the glass sheet Afrom the table 6, and the loader and unloader may have an industrialcylindrical coordinates robot etc. as their major component.

FIG. 2 is an overall oblique view showing the relationship between thedie 40 and the table 6. A pair of groove and rail guides 4 are providedon the bench 2, and the table 6 is mounted on the groove and rail guides4, with the top surface of the table 6 being a suction surface. Thetable 6 can move freely on a horizontal plane along the pair of grooveand rail guides 4, i.e. a linear slider, in two opposite directions.

The pair of groove and rail guides are housed inside a casing 12, alongwith an advancing mechanism. The casing 12 stretches along the grooveand rail guides 4. The advancing mechanism has a feed screw 14comprising a ball screw as shown in FIG. 1. The feed screw 14 (FIG. 1)is located underneath the table 6, is screwed and extends through anut-like connector 16 (FIG. 1) which is joined onto the stem 8. The twoends of the feed screw 14 are allowed to rotate freely, supported bybearings which are not shown, and an AC servomotor 18 (FIG. 1) isconnected to one end. The smallest possible openings are provided on thetop surface of the casing 12 to allow the movement of the stems 8.

The casing 12, with its very small openings, completely covers thegroove and rail guides 4, feed screw 14, etc. thus dramatically reducingthe escaping and scattering of the dust generated by the feed screw 14etc. and preventing coating liquid dripping from a height above thetable 6 from undesirably reaching the feed screw 14 and groove and railguides 4. Furthermore, by drawing out the air inside the casing 12 andthus bringing the air pressure there down to a negative value, it ispossible to increase the cleanliness of the atmosphere during theapplication of coating liquid and dramatically reduce the occurrence ofdefects, as this, along with the small size of the openings, will tendto prevent the dust generated inside the casing 12 from escaping, whilesucking in the dust floating outside.

A sensor support 20 is placed on the top surface of the bench 2. Thesensor support 20 has an inverted L-shape, and its end extends to apoint right above one of the groove and rail guides 4. Anelectric-motor-driven lifting actuator 21 is mounted at the end of thesensor support 20, and a thickness sensor 22 is secured onto the liftingactuator 21 facing down. The thickness sensor 22 may be a laserdisplacement gauge, electronic micro-displacement gauge, ultrasonicthickness gauge or the like.

Also, an inverted L-shaped die support 24 is placed on the top surfaceof the bench 2, at a location closer to the center of the bench 2 thanthe sensor support 20. A lifting mechanism 26 is mounted at the end ofthe sensor support 24, and, although not shown in detail in FIG. 2, thelifting mechanism 26 is equipped with a lifting bracket which is engagedwith a pair of guide rods in such a way that it can move up and downfreely. A feed screw comprising a ball-screw is provided between theguide rods, and the feed screw is screwed through the lifting bracket.The upper end of the feed screw is secured onto a casing 28 whichaccommodates the guide rods and feed screw, via a bearing in such a waythat it can rotate freely, and its top portion is connected to the ACservomotor 30.

An U-shaped die holder 32 is mounted on the lifting bracket in such amanner that it can freely rotate in the vertical plane, and the dieholder 32 stretches horizontally straddling the pair of groove and railguides 4. A little above the die holder 32, a horizontal bar 36 issecured onto the lifting bracket, with the horizontal bar 36 stretchingalongside the die holder 32. Adjustment actuators 38a and 38b which aredriven by air pressure are mounted at either end of the horizontal bar36. Each of the adjustment actuators, 38a and 38b, has an extendible rodwhich protrudes from the bottom surface of the horizontal bar 36, andthe two rods extend to touch the die holder 32 near its ends.

Inside the die holder 32, a die 40 is mounted as a means of dischargingthe coating liquid.

As is clear from FIG. 2, the die 40 lies over the pair of groove andrail guides 4, stretching horizontally in the width direction, i.e.perpendicular to the traveling path of the table 6. The horizontal leveladjustment of the die 40 can be carried out by extending or retractingthe extensible rods of adjustment actuators 38a and 38b which aremounted at both ends of the horizontal bar 36, and rotating the dieholder 32 around its rotational axis, thus maintaining the bottomsurface of the die 40 and the top surface of the table 6 parallel toeach other.

A distance sensor 6m comprising an electromagnetic induction typesensor, electronic micro-displacement gauge, etc., for measuring thedistance between the bottom surface of the die 40 and the top surface ofthe table 6, is mounted on the table 6 at each of its upstream sidecorners with respect to the coating direction. Other possible choicesfor the distance sensor 6m include a photoelectric sensor, ultrasonicsensor and differential transformer type contact sensor. The die ismounted in such a way that it can freely rotate around an axis which isparallel to the longitudinal axis of the die, and consideration has beengiven to facilitate the discharge of air trapped inside the die bydischarging the coating liquid from the discharge outlet 66 (FIG. 3)facing upwards.

The details of the die 40 are given in FIG. 3, in which the rotationalaxis of the die holder 32 and that of the die 40 are shown with a chainline. The die 40 has a front lip 58 and a rear lip 60 which are slenderblocks extending in the width direction of the die. The lips 58 and 60are put firmly together in the traveling direction of the table 6 withthe front lip in front. In the middle of the die 40, a manifold 62 hasbeen formed, and the manifold 62 stretches in the length direction ofthe die 40. The manifold 62 is permanently connected to the coatingliquid supply hose 42 via an internal passage. The cross-sectional shapeof the manifold may be a circle such as the one shown in FIG. 3,semi-circle, inverted triangle, or any other shape which is wider thanthe gap LP of the slot 64 and capable of holding a liquid. Concerningthe lengthwise changes in cross-section of the manifold, thecross-section may be the same throughout its length, i.e. so-celledT-shape manifold, or may gradually increase towards the middle in thelength direction of the die to ensure a smooth flow, i.e. so-calledcoat-hanger type or fish-tail type.

The slot 64 extends vertically downwards from the manifold 62, and opensthrough the bottom surface of the die 40. The bottom opening of the slot64, i.e. the discharge outlet 66, extends in the length direction of thedie 40, in the same manner as the manifold 62. More specifically, a shim(not shown on the drawing) is placed between the front lip 58 and rearlip 60, and the thickness of the shim is used to adjust the gap LP ofthe slot 64, i.e. the length of the discharge outlet 66 in the travelingdirection of the table 6, to, for example, 0.1 mm.

When looking in the forward traveling direction of the table 6 (the onemarked "B" in FIG. 3), i.e. the direction in which the table 6 at itsinitial position as shown in FIG. 1 moves towards the die 40, the lowerpart of the front face of the front lip 58 which is situated at thefront is shaped into a downward slope 68 inclined towards the dischargeoutlet 66, and the bottom surface 70 of the front lip 58 is defined bythe surface which lies between the lowest edge of the slope 68 and thedischarge outlet 66. Similarly, the lower part of the rear face of therear lip 60 is shaped into a downward slope 72 inclined towards thedischarge outlet 66, and the bottom surface 74 of the rear lip 60 isdefined by the surface which lies between the lowest edge of the slope72 and the discharge outlet 66.

As is clear in FIG. 3, the length L_(R) of the bottom surface 74associated with the rear lip 60 in the traveling direction of the table6 is greater than the length L_(F) of the bottom surface 70 associatedwith the front lip 58, and these bottom surfaces 70 and 74 lie in thesame horizontal plane.

For example, the length L_(F) of the bottom surface 70 is set to0.01-0.5 mm, and the length L_(R) of the bottom surface 74 is set to 1mm or more and 4 mm or less.

Moreover, the angle θ_(F) made by the sloped surface 68 associated withthe front lip 58 and a horizontal plane which intersects with it is setbetween 30° or more and 60° and less. On the other hand, there is noparticular constraint on the angle θ_(R) between the sloped surface 72associated with the rear lip 60 and the horizontal plane, although itshould preferably be set in a similar range to θ_(F).

To ensure fast response of coating liquid discharge from a coatingliquid discharger in the above configuration, it is necessary to securefirm sealing throughout the coating liquid delivery piping system.Although there is no particular limit on the thickness of the coating Dwhich can be produced, the applicator can be used most favorably for theproduction of thin-film coatings within the range of 1-500 μm inthickness after application and before drying. When the thickness of thecoating D is less than 1 μm, it is difficult to obtain high uniformitydue to restrictions in machining accuracy for the die 40 and thicknessaccuracy of the substrate A. Although it is of course applicable tocases where the coating thickness exceeds 500 μm, such an applicationwill not markedly reflect the meritorious effects of the presentinvention.

The uniformity of the coating D is controlled by adjusting the slot gapL_(P) of the die 40 or the clearance L_(C), i.e. the length of the gapbetween the die 40 and the substrate A, as shown in FIG. 3. In thepresent invention, there are no particular restrictions as to the slotgap L_(P) and clearance L_(C), but the slot gap L_(P) is preferably setin the range of 10-500 μm. Otherwise, the adverse effects of variance ingap lengths and undulations will be extremely great, as it is difficultto produce a die 40 to maintain a slot gap of less than 10 μm with highaccuracy. Further, the clearance L_(C) is preferably set in the range of10 μm-1 mm, since maintaining a clearance L_(C) of less than 10 μm withhigh accuracy is difficult due to constraints in the machining accuracyof equipment and substrates A. The clearance L_(C) is also preferably 1mm or less in view of maintaining the stability of the coating liquidbead C. Also, to obtain a highly uniform coating D by producing a stablecoating liquid bead C, the clearance L_(C) is preferably maintainedprecisely within an overall range of 1.2 to a few tens of times thecoating thickness. A pressure chamber may be provided at the rear lip 60side to adjust the positive or negative pressure on the upstream sidesurface of the coating liquid bead C as a means of facilitating theformation of a stable coating liquid bead C.

The slot gap variation in the width direction of the die can be freelyadjusted using adjustment bolts, not shown in the drawing.

The coating method will now be explained with reference to typical timecharts shown in FIG. 4, where Chart a represents the time chart of tabletravel, with the top half of the chart indicating forward movement andthe bottom half of that indicating backward movement. Charts b and cshow changes in the operation of adhering the substrate to be coated bysuction and the operation of the lift pins for the table 6 (not shown inthe drawing) with time, respectively, while Chart d indicates pressurereduction action in a case where a pressure reduction chamber isprovided at the rear lip side of the die 40. Charts e and f illustratethe wiping action for the die 40 and the vertical movement of the die40, respectively, while Chart g shows the operation of theelectromagnetic changeover valve 46, with the top half of the chartindicating changeover to the coating die side and the bottom half ofthat to the coating liquid tank side. Chart h illustrates the operationof the syringe pump 44, with the top half of the chart indicatingdischarge and the bottom half of that indicating suction. Chart iexplains an overall sequence of operations.

Although not shown in the drawing, there is a sensor which detects theposition of the table 6 or that of the substrate A to be coated. Thissensor may comprise a proximity sensor, photoelectric sensor or thelike, or may be based on an encoder which detects the amount ofrevolutions made by the table-driving motor.

FIG. 5 shows an overall configuration of the wiping device.

This device makes the bottom surfaces 70 and 74 as well as the slopedsurfaces 68 and 72 of the die 40 substantially even by wiping offleft-over coating liquid using a plastic or rubber wiper 102, which is,after being pushed up via a cylinder 118 and pressed against these threesurfaces at a predetermined pressure, moved towards one end of the die40 in the width direction by means of a driving system comprising amotor 112 and a ball screw 114.

The coating liquid 120 thus removed is collected in a tray 104, whichretains the wiper 102 and moves along with it, and is collected bysucking it into a waste liquid tank 108 via drainage piping 106 using apump 110. A tray 104 can also be used for the collection of excesscoating liquid generated during the non-coating period.

As is shown in the time charts given in FIG. 4, after resetting all thecomponents of the coating apparatus to their respective originalpositions, the electromagnetic changeover valve 46 is changed over tothe coating liquid tank 50, and suction operation is carried out usingthe syringe pump 44. After that, with the lift pins raised, thesubstrate A to be coated is transferred onto the lift pins from theloader, not shown in the drawing, and is placed onto the table 6 at apredetermined location by lowering the lift pins. The substrate A to becoated is then immobilized on the table 6 by means of vacuum suction.Apart from vacuum suction, a pinching lever based on a link mechanism,suckers, an adhesive sheet, etc. may also be used as a means ofimmobilizing (retaining) the substrate A on the table 6, and these arealso included in the "means of retaining" as defined in the presentinvention.

After a predetermined amount of the coating liquid is sucked into thesyringe pump 44 from the coating liquid tank 50, the electromagneticchangeover valve 46 is switched over to the die 40. The table 6 is movedin the forward direction to carry the substrate A to a position justbelow the die 40, where the forward traveling of the table 6 is stopped.The stopping position is determined by receiving a signal transmittedfrom the position sensor 57. The die 40 is then lowered, and apredetermined clearance L_(C) is secured by means of a linear sensor ora positioning mechanism such as cotters. Instead, the substrate A to becoated may be moved in after lowering the die 40. After this, thedischarge of coating liquid is started by activating the syringe pump 44to supply coating liquid to the die 40, practically at the same time asthe securing of the clearance L_(C), and a predetermined coating bead C(FIG. 3) is formed between the die 40 and the substrate A throughout thewidth by keeping the table 6 at rest for a predetermined period afterthe beginning of the discharge of the coating liquid.

In FIG. 3, the volume V (in mm³ or μl) of the coating liquid dischargedfrom the discharge slot during the period where the table remains atrest after the beginning of discharge is preferably within the rangegiven by the following formula:

    L.sub.P ×L.sub.C ×W≦V≦(L.sub.F +L.sub.P +L.sub.R)×L.sub.C ×W,

where L_(F) (mm) is a length of the bottom surface of the front lip;L_(R) (mm) is a length of the bottom surface of the rear lip; L_(P) (mm)is a width of the slot exit aperture; L_(C) (mm) is a distance betweenthe slot exit aperture of the coating liquid applicator and thestart-of-coating line on the substrate to be coated; and W (mm) is alength of the slot exit aperture in the direction perpendicular to thecoating direction.

Namely, to ensure the formation of a satisfactory coating liquid bead,the volume of coating liquid V is preferably (L_(P) ×L_(C) ×W) or more,and, to prevent inconsistency in coating thickness resulting from athick coating at the start-of-coating line due to the outflow of thecoating liquid from the space defined by the bottom surface 70 of thedie 40 and substrate A to be coated, the volume of coating liquid V ispreferably [(L_(F) +L_(P) +L_(R))×L_(C) ×W] or less.

After thus forming a coating liquid bead C, coating is started by movingthe table 6 in the forward direction at a predetermined speed. Thecoating liquid bead C may be stabilized by reducing the air pressure inthe pressure reduction chamber provided at the rear lip side of the die40 to a predetermined value below the atmospheric pressure almost at thesame time as the beginning of coating. With this stabilization of thecoating liquid bead C, it is possible to quickly equalize the amount ofthe coating liquid consumed in the coating operation with that suppliedvia the discharge outlet 66 of the die 40, and achieve the normalcoating condition quickly, thus enabling the production of a stablecoating within a short period after the beginning of application.

Coatings are produced using the squeegee coating method, in which thesupply of coating liquid by the syringe pump 44 is stopped when thesubstrate A to be coated arrives at a location which is a predetermineddistance before the end-of-coating line, to finish off coating byconsuming the coating liquid stored in the bead C. Instead, the supplyof coating liquid may be stopped when the substrate A to be coatedreaches the end-of-coating line.

If necessary, a predetermined amount of already discharged coatingliquid may be recovered by suction via the discharge outlet 66 of thedie 40 by reversing the operating direction of the syringe pump 44 whenthe substrate A to be coated reaches the end-of-coating line. In thatcase, the substrate A to be coated may temporarily be stopped at theend-of-coating line to ensure complete recovery of the coating liquidbead.

Coating is ended by raising the die 40 when it comes near theend-of-coating line in order to distance it from the coated substrate A.After that, the coating liquid is discharged by operating the syringepump 44 to eliminate any discontinuity which may have been created atthe discharge outlet 66 due to the recovery by suction of the coatingliquid. The table 6 continues traveling in the forward direction, andthe table stops when it reaches a predetermined point where thesubstrate A is transferred to the next process. There, the substrate Ais raised by lifting the lift pins, with vacuum suction released, and atthis position the substrate A is passed on to the unloader (not shown inthe drawing). At the same time, the coating liquid left over on the slotexit surface of the die 40 is removed by wiping the die 40 after a smallamount of liquid is discharged by the syringe pump 44. The table 6 thentravels backwards, and returns to the original position to be loadedwith a next substrate A to be coated. This marks the end of a coatingoperation cycle, and the equipment will start another coating operationcycle for a next substrate A.

In this coating process, coating may be finished with squeegee coating,without the reverse direction operation of the syringe pump at theend-of-coating line.

With this coating procedure, the clearance is accurately set bycontrolling the descent of the die 40 based on output signalstransmitted from a distance sensor (not shown in the drawing) whichmeasures the distance between the table 6 and die 40, while taking intoaccount the thickness of the glass substrate A measured using thethickness sensor 22. Instead, the die 40 may be lowered to thepredetermined position based on output signals transmitted from a linearsensor which measures the position of the die holder which supports thedie 40.

The measurement of the thickness of the glass substrate A is carried outwhen loading of the glass substrate A is completed by securing it on thetable 6 via suction, with the thickness sensor 22 moved down to apredetermined position. After measurement, the thickness sensor 22 ismoved back to the original position.

The above sequence of operations makes it possible to determine thebeginning and end of the coating area on the substrate A, since thecoating operation takes place with the table 6 moved forward only afterit is stopped at the start-of-coating line to ensure that a coatingliquid bead C with a shape necessary for stable coating production isformed throughout the required coating width. It also makes it possibleto dramatically reduce the distance from the edge of the substrate A tothat of the area on which a usable coating can be formed (regularcoating thickness area), since it can greatly reduce the variations incoating thickness at the beginning and end of the coating area from thecoating thickness in the steady-state coating region to which thesteady-state coating is applied, thus allowing the portion of thesubstrate A on which a useful coating can be produced to be increased interms of the ratio of its length to the entire substrate length.

FIG. 6 shows another practical embodiment of the coating apparatus shownin FIG. 2.

In this embodiment, a pair of widthwise positioners 200 which determinethe widthwise position of the substrate A are added. Each widthwisepositioner 200 which is placed at each lateral side of the substrate Acomprises a positioning pusher 202 made of a resin etc. which is pressedagainst one of the edge surfaces of the glass substrate, a guide 204which guides the positioning pusher 202 bi-directionally in thewidthwise direction, a stopper 206 which is capable of holding down thepositioning pusher at any given position for adjustment, and a bracket208 which supports the moving parts and connects and secures them ontothe bench 2.

The positioning pusher 202 moves back and forth powered by a drivingactuator, such as an air cylinder or a linear motor, not shown in thedrawing. The widthwise distance between the pair of positioning pushers202, which is adjusted by means of the stoppers 206, is preferably 0.1-2mm greater than the width of the substrate A. Adjustment to less than0.1 mm would be difficult, while positioning would not be effective ifthe difference was 2 mm or greater. The elimination of the gap betweenthe substrate to be coated and the positioning pusher is preferablyavoided, since it would subject the substrate to abnormal forces, unlessa mechanism which absorbs these forces is added or an elastic materialis used for the positioning pushers.

Using a loader, the substrate A is transferred from the previous processand loaded onto the table 6 at its initial position, where the entirewidthwise positioner assembly is arranged in such a way that the pair ofthe positioning pushers 202 are placed roughly symmetrically withrespect to a datum line chosen to coincide with the center line in thetraveling direction at the loading location (for example, the centerline of the discharge outlet 66 of the die 40). It is highly preferablethat the positioning error for this be limited to within ±1 mm.Otherwise, the intended coating area on the substrate A would be shiftedgreatly, and the widthwise coating thickness profile within the intendedcoating area would be uneven.

Here the thickness sensor 22 is shifted towards the die 40, along withits associated L-shaped sensor support 20 etc., from the position asshown in FIG. 2, to prevent it from interfering with a loader and thesubstrate A to be coated when the substrate A is loaded onto the table.

In the embodiment shown in FIG. 6, a thickness sensor 22 is located at aposition where the thickness of the substrate A around its center can bemeasured when the substrate A comes to a stop with the beginning of itscoating area lying just below the discharge outlet of the die 40. Sincethe substrate A is not raised or lowered at this position, the distancebetween the thickness sensor 22 and the substrate A can be fixed to avalue most suitable for measurement, and a lifting mechanism for thethickness sensor 22 is not necessary.

The coating method which utilizes this coating apparatus will now beexplained.

Upon resetting all the moving parts of the coating apparatus, the table6 and die 40 move to their respective standby positions. By this time,the coating liquid supply system, from the coating liquid tank 50 to thedie 40, is already filled with coating liquid, with the so-called airpurge operation also completed in which any air remaining in the die isdischarged by turning the die over and discharging the coating liquidupwards. The lift pins are raised from the surface of the table 6, notshown in the drawing, and stand by to receive a substrate to be coatedfrom the loader not shown in the drawing.

The substrate A is then loaded onto the top of the lift pins from theloader. This loading position is just above the predetermined positionon the table 6 for loading, and the loading is carried out within apositioning accuracy of ±1 mm in the traveling direction. This uniquelydefines the relative geometrical relationship between, substrate A andthe table in their traveling direction. As a result, moving thestart-of-coating line on the substrate A right under the dischargeoutlet of the die 40 becomes synonymous with moving the table 6 into itscorresponding position, and this makes it possible to carry out theposition control accurately, based on outputs of the encoder secured tothe feed screw 14 or table position sensor, without directly measuringposition of the substrate.

The substrate A on the lift pins is then placed onto the top surface ofthe table by lowering the lift pins, and is sandwiched, from both sideswidthwise, by a pair of positioning pushers 202, thus limiting thewidthwise positioning error from the intended coating area on thesubstrate A relative to the widthwise position of the discharge outlet66 of the die 40 to within ±1 mm.

In this case, too, the widthwise relative geometric relationship of thetable 6 and die 40 are uniquely determined.

After the completion of sandwiching between the pair of positioningpushers 202, the substrate to be coated is immobilized via suction,while the positioning pushers 202 are moved away outwards. When thereturning of positioning pushers 202 to its initial position is detectedby position sensors, not shown in the drawing, the table 6 is stoppedafter being moved to a position which is predetermined based on itsrelative geometrical relationship with the substrate, and this ensuresthat the start-of-coating line on the substrate mounted on the table isplaced right under the discharge outlet of the die 40 with a positioningaccuracy of within ±1 mm, preferably ±0.5 mm. While at rest, thethickness of the substrate A is measured using the thickness sensor 22.Based on this thickness and a predetermined clearance, the requiredvalue for a descent of the die 40 in terms of the reading on the linearsensor is calculated, and then the die is controlled so as to move tothe calculated position, ensuring that the die 40 descends to theposition calculated above on the linear sensor, with the clearancebetween the substrate to be coated and the die set accurately.

By this time, the syringe pump 44 has finished drawing a predeterminedamount of coating liquid from the coating liquid tank, and, afterensuring of the establishment of the clearance, coating liquid issupplied to the die 40 from the syringe pump. As soon as the syringepump is activated, the timer inside the computer 54 is started, and,after a predetermined period of time, a starting signal is sent to thesequencer 56 from the computer. The table 6 then starts moving at thecoating speed, and coating begins.

Since the substrate A is always mounted in the same predetermined placeon the table 6, it is possible to set the position sensors or thereading of its associated encoder to the position of the table 6corresponding to (a) 5 mm before the end of the intended coating area or(b) the end of the intended coating area on the substrate in thetraveling direction. When the table 6 comes to a position correspondingto (a), a stop signal is sent by the computer 54 to the syringe pump 44to operate squeegee coating until reaching the position (b), and as soonas reaching to the position (b), the computer 54 sends a signal to raisethe die 40, which leads to raise the die 40, thus disconnecting thecoating liquid bead completely.

While these operations are taking place, the table 6 continues moving,but finally stops when it reaches a terminal position where thesubstrate A to be coated is transferred using an unloader. Then theimmobilization by suction of the substrate A is disabled, and thesubstrate A is raised by lifting the lift pins.

The substrate A is then secured from below by an unloader, not shown inthe drawing, and is handed over to the next process. After passing thesubstrate on to the unloader, the lift pins are lowered and the table 6returns to its original position.

The syringe pump 44 is activated again and a small amount of coatingliquid, 10 μl-500 μl, is sent to the die 40 to ensure that there are novoids between the lips of the die 40. After covering the bottom surfaceof the die 40 with coating liquid, any residual coating liquid remainingon the bottom surface of the die 40 is wiped off with a wiper made ofsilicone rubber or the like, thereby making the surface substantiallyeven. If the bottom surface of the die is not covered with coatingliquid, residual coating liquid tends to be left in isolated patches,and attempts to wipe this off with a rubber wiper tend to leave rubberdusts as a pollution source, which, in turn, give rise to coatingdefects.

The 10-500 μl mentioned above is a discharging volume suitable forcovering the entire bottom surface, which makes the wiping operationpossible to clean the bottom surface without generating rubber dusts,with the coating liquid acting as a lubricant.

After the syringe pump 44 has discharged the coating liquid to be wipedoff, it is filled up with another volume of coating liquid from the tank50 again via suction. It then stands by for a next substrate to becoated and the same operations are repeated.

In the above embodiment, when the substrate to be coated which has beenpassed on from the loader to the lift pins was placed onto the surfaceof the table 6 by lowering the lift pins, if the lift pins are retractedtoo fast, part of the air between the substrate and the surface of thetable 6 sometimes fails to escape resulting in the substrate floating onthis layer of air due to a phenomenon called the air bearing effect, andthe position of the substrate could shift greatly in the travelingdirection from the predetermined position.

For this reason, the surface of the table 6 is preferably subjected tovacuum suction through the suction holes of the substrate at -50 to -300mmHg before the lowering of the lift pins. If the lift pins are loweredunder this condition, the air between the substrate and the surface ofthe table 6 is removed effectively irrespective of the lowering speed ofthe lift pins, which prevents the substrate from moving on the surfaceof the table 6, leading to accurate positioning of the substrate at thepredetermined position on the table 6. If the above suction pressure isless than -50 mmHg, it will have no air removal effect, while, if it isgreater than -300 mmHg, the suction pressure will be too high for thesubstrate and difficult to move the substrate widthwise to thepredetermined position when activating the widthwise positioner.

Improvements on the ±1 mm positioning accuracy, e.g. to not more than±0.5 mm, can easily be achieved widthwise by improving the accuracy ofthe setting of the widthwise distance between the pair of thepositioning pushers 202 of the widthwise positioner. However, in thetraveling direction, it is difficult to always guarantee a ±0.5 mmaccuracy, as the transfer of the substrate from the lift pins to thesurface of the table 6 is vulnerable to disturbance, even where itstransfer from the loader to the lift pins can be carried out with thisaccuracy.

Therefore, to achieve this accuracy in the traveling direction, it isnecessary to undertake positioning in this direction after placing thesubstrate onto the surface of the table 6, as in the case of the widthdirection.

FIGS. 7 and 8 show such embodiment examples. FIG. 7 is a plan viewlooking down at the table 6 from above, and shows the relative positionsof a traveling direction positioners 220 and the widthwise positioners200.

The traveling direction positioners 220 are the ones which comprise apair of the widthwise positioners 200 secured to the table, but are insuch a way that they sandwich the substrate in the traveling direction.Like the widthwise positioner 200, each traveling direction positioner220 comprises a positioning pusher 222, a guide 224 which guides thepositioning pusher 222 in the traveling direction, a stopper 226 whichis capable of holding down the positioning pusher at any given positionfor adjustment, a bracket which, not shown in the drawing, secures theunits mentioned above onto the edge faces of the table 6, and a drivingactuator which, not shown on the drawing, moves the positioning pusher222 in the traveling direction reciprocally.

As shown in FIG. 7, the traveling direction positioners 220 are placedin front of and behind the table 6 and they are arranged in such amanner that they sandwich the substrate in the traveling direction,leaving a gap of 0.1-1 mm. Further, it is possible to place thesubstrate in a predetermined position on the table 6 with an accuracy of±0.5 mm, by arranging and adjusting the pair of the traveling directionpositioners 220 and the substrate in such a manner that they are placedapproximately symmetrically with respect to a line drawn at the centerof the loading position in the widthwise direction.

Regarding positioning order, the traveling direction and the widthwisedirection positioning may be undertaken simultaneously, or one of themis performed first, followed by the other operation.

FIG. 8 is a plan view looking down at the table 6 of another embodiment.

In this embodiment, an adjustment piece 210 made of a resin is attachedto the tip of the positioning pusher of the widthwise positioner 200.The adjustment piece 210 is designed so that the distance between thetransverse sides 216a and 216b is greater than the length of thesubstrate in the traveling direction by 0.1 mm-1 mm, while the distancebetween the pair of longitudinal sides 214 of the adjustment piece whichsandwich the substrate in the widthwise direction, is greater than thelength of the substrate in the width direction by 0.1-1 mm by adjustingthe stopper 206.

The entire widthwise positioner 200 assembly is arranged and adjusted insuch a manner that, when the substrate A to be coated is sandwiched bythe pair of adjustment pieces 210, the deviation in the position of thesubstrate on the table 6 from the predetermined position is within ±0.5mm.

If this positioning device 218 is activated after the substrate to becoated has been transferred from the top of the lift pins onto thesurface of the table 6, the edges of the substrate to be coated come incontact with sloped sides 212 of the adjustment pieces 210 as the pairof adjustment pieces 210 moves towards the center, and the substrate tobe coated moves into the final position with its edges sliding againstthe sloped sides as a guide, which finally leads to positioning of thesubstrate with a margin determined by the gaps made by transverse sides216a and 216b and longitudinal sides 214.

The preferable inclination of the sloped sides is in a range of 5°-45°with respect to the transverse sides. If the inclination is less thanthis range, the sloped side will become too long, increasing the size ofthe device, and if it is greater than this range, the substrate to becoated fails to slide the slop sides and gets stuck, spoiling theguiding effect of the slope. Also, if adjustment pieces 210 of variousdimensions in terms of the lengths of the transverse sides 216a and 216bare prepared in advance and made readily interchangeable, they could beeasily applied to different sizes of substrates.

This embodiment makes it possible to simultaneously carry out thepositioning of the substrate on the table 6, both in the widthwise andtraveling directions, with a high accuracy with less components than theembodiment shown in FIG. 7. Alternatively, the positioning device 218may be fixed at the position which the substrate to be coated will besandwiched between them before the substrate on the lift pins is loweredonto the table 6.

FIG. 9 shows still another embodiment, in which a rectangular depression240 is provided in a predetermined position in the surface of the table6. At the base of the depression, suction holes 244 and four lift pins(not shown in the drawing) are provided, and the width L_(w) and thelength in the traveling direction Ll of the bottom of the groove aregreater than the corresponding dimensions of the substrate by about0.1-1 mm. The depth Lh of the depression 240 is made equal to or lessthan the thickness of the substrate to be coated. The widthwise lengthand traveling direction length of the depression 240 increase graduallyfrom the base 246 of the depression 240 to the surface of the table 6,making slopes 242 and 248. These slopes function as a guide whenlowering the substrate on the lift pins, and the eventual positioningaccuracy is determined by the gap between the substrate and bottom 246of the groove.

While in the embodiments mentioned above, the total length of thepressing portion of the positioning pusher 202 may be either longer orshorter than the length of the corresponding side of the substrate to becoated, it is preferrable to press positions closer to the four cornersof the substrate A resulting in the smaller skew of the substrate withthe same gap setting. When the degree of this skew is great, thesubstrate to be coated is placed obliquely with respect to the dischargeoutlet of the die 40, and, in extreme cases, the beginning of the coatedarea becomes an oblique line on the substrate.

While the thickness sensor 22 is placed at a point sufficiently remotefrom the substrate loading location in the traveling direction to avoidinterference which may occur during the loading of substrate onto thetable 6 in the above description, it is possible to locate the thicknesssensor 22 upwards, which could eliminate such interference, even if thisconfiguration is done at the substrate loading portion. In this case,the thickness sensor 22 is moved by means of a lifting mechanism, and islowered when a measurement is to be made. Therefore, the thickness ofthe substrate can be measured freely, no matter whether the substrate ison the loader, lift pins or the surface of the table 6. In particular,if a measurement of the thickness of the substrate to be coated can bemade while the substrate is on the loader, the thickness of thesubstrate to be coated can be measured independent of the movement ofthe table 6, thus contributing to a reduction in cycle time andimprovement in productivity.

In an attempt, coating was performed under the coating conditions ofExample 1 given below, except that the entire surface of a glasssubstrate was coated, with the syringe pump stopped 5 mm before the endof the coating area, and that squeegee coating was carried out bykeeping the table moving until it reached the transferring positionwhere an unloader is provided. FIGS. 10 and 12 are coating thicknessprofiles in the traveling and width directions of the table 6respectively, with positioning performed. FIGS. 11 and 13 are coatingthickness profiles in the traveling and width directions of the table 6respectively, without positioning performed. When positioning was notperformed, there were deviations of 1.5 mm in the traveling directionand 2 mm in the width direction from the reference point, while theyboth ended up to 0.2 mm when positioning was carried out.

With positioning performed, coating thickness profiles shown in FIGS. 10and 12 can be consistently obtained with 100 substrates, while, withoutpositioning, fluctuation in coating thickness profiles increases as thenumber of substrates increases. The largest fluctuation examples areshown in FIGS. 11 and 13, which exhibit the tendency that, when thecoating is thick at one end of the coating area, it will be thin at theother end, with the usable coating area reduced in which coatingthickness is uniform.

Apart from a shift in the coating area, omission of positioning tends tohave adverse effects on the coating thickness profile within the coatingarea, reducing the stability and reproducibility in coating accuracy.

Incidentally, coating apparatus to produce a coating D on a substrate Ahas a die 40 with a shape as shown in FIG. 3, so that it can produce auniform coating D and is suitable for manufacturing coated sheetproducts such as color filters. Namely, with the die 40, the lengthL_(R) of the bottom surface 74 of the lip 60 is preferably longer thanthe length L_(F) of the bottom surface 70 of the front lip 58, as thisensures that the boundary line E of the coating liquid bead C (see FIG.3) is maintained at the bottom surface 70. This prevents fluctuations inthe shape of the coating liquid bead C during the formation of thecoating D, and makes the coating D uniform. With this type of die, thelength L_(F) of the bottom surface 70 is preferably 0.01 mm or largerand 0.5 mm or smaller. If the length L_(F) is 0.5 mm or less, it cancertainly prevent the border line E of the coating liquid bead C fromgoing over the edge of the bottom surface 70 due to surface tension andflowing up to the front of the front lip 58. In order to reduce thelikelihood of the border line E of the coating liquid bead C flowing upto the sloped surface 68, the angle θ_(F) made by the sloped surface 68which connects to the bottom surface 70 and a horizontal plane ispreferably 30° or greater, while, to maintain the stiffness of thebottom portion of the front lip 58, this angle θ_(F) due to the slopedsurface 68 is preferably 60° or smaller.

If the border line E of the coating liquid bead C flows up to the frontof the front lip 58, it is impossible to keep the coating D thin. Thelength L_(F) of the bottom surface of the front lip 58 is preferably atleast 0.01 mm. If it is close to zero, i.e. the bottom of the lip beinga knife-edge, it will be difficult to maintain its stiffness and keep iton the same plane as that containing the bottom surface of the rear lip60 in the direction of the width.

If the bottom surface 70 of the front lip 58 and bottom surface 74 ofthe rear lip 60 lie on the same horizontal plane, the two border linesassociated with them which define the upper end of the coating liquidbead C can be stably maintained, and the shape of coating liquid bead Cwill not become unstable.

The bottom surface 74 of the rear lip 60 is preferably 1 mm or greaterand 4 mm or smaller, as this will ensure the formation of a coatingliquid bead between the bottom surface 74 and the substrate A to becoated. If the L_(R) is smaller than 1 mm, the bead formation effectwill be insufficient, while, if it is greater than 4 mm, the size of thebead will not increase further, so that there will not be muchadvantage.

While a die of the embodiment described above is most suitable for theproduction of a coating on sheet substrates such as glass sheets, it isalso applicable to continuous application of coating liquid on longsheet substrates and coating on continuous substrates. Also, in theabove embodiment, the die is placed face down, but, even if it is placedon its side or face up, uniform coatings can be produced on substratesin the same manner.

While the preceding die embodiments represent the preferred ones,coating apparatus according to the present invention will also provequite effective with other types of dies.

Coating accuracy will increase as the clearance L_(C) between the die 40and the substrate A to be coated becomes more uniform in the directionof the length of the die.

Adjustment of the clearance is undertaken during the preparatory stepbefore coating, rather than during coating. The adjustment procedurewill now be explained with reference to the flowchart shown in FIG. 14.

Firstly, prior to the beginning of a continuous coating operation (e.g.immediately after the completion of the assembly of coating apparatus,replacement of the die 40 or the like), the table 6 in FIG. 2 is movedto bring the pair of distance sensors 6m attached to it to a positiondirectly below the die 40, and stopped. After the die 40 is lowered tothe measurement position and stopped, the distances Ga and Gb which aredefined as length between each distance sensors and predeterminedpositions on the bottom surface of the die 40 are measured by the pairof distance sensors 6m. When the two distances differ, adjustments aremade to bring them in line by allowing the die 40 to be rotated by meansof adjustment actuators 38a and 38b which correspond to Ga and Gbrespectively. More specifically, if Ga>Gb, the extensible rod of theadjustment actuator 38a is moved downwards, and that of the adjustmentactuator 38b is moved upwards. If Ga<Gb, the opposite operations areperformed. In this manner, the bottom surface 70 of the die 40 isbrought into parallel position with respect to the top surface of thetable 6. The distance measurement reading Ga or Gb when parallelism isachieved is relabeled as L0. The reading of the linear sensor for thedie holder 32 which measures its travel distance associated with thelifting and lowering of the die 40 is labeled as L1. Then, from L0 andL1, the expected linear sensor reading when the bottom surface 70 of thedie 40 comes right on the top surface of the table 6, labeled as L2, iscalculated. Based on L2, the expected linear sensor reading for theposition of the die 40 during coating, labeled L3, is calculated, takinginto account the thickness of the substrate and clearance. With acalculation means which carries out these calculations, along with acontrol means which actually moves the die 40 down to the pointcorresponding to the linear sensor reading L3, the clearance can be setaccurately for dies of any dimensions. Namely, if the shape of the dieas well as the distance from the die holder 32 to the bottom surface ofthe die 40 changes, the parallelism between the die and the table can beaccurately adjusted, while the clearance can be set accurately accordingto the glass substrate to be coated.

Although, in the above embodiment, parallelism is adjusted after haltingthe downward movement of the die and measuring the distances Ga and Gb,such adjustment may be undertaken simultaneously with the measurement ofGa and Gb while the die is being lowered.

While improvements in the accuracy of the clearance in the travelingdirection increase the accuracy and stability of the coating, anembodiment according to the present invention has roller bearings as alinear slider which shoulder the table 6 and guide its movement as partof the linear slider.

Namely, the above linear slider 400 comprises a pair of V-shaped grooves402 provided on the top surface of the bench 2, V-shaped roller bearings404 housed in the V-shaped grooves 402, a table 6 with its stems 8shouldered by the roller bearings 404, a ball screw nut 412 provided ina predetermined position on the bottom surface of the table 6, and ballscrew 416 which, turned by a driving motor 18, engages with the aboveball screw nut 412, as shown in FIG. 15 illustrating enlarged images ofthe main components. The above ball screw nut 412 is coupled to a ballscrew support 420 which is coupled to the table 6 via a coupler 414which is provided only locally and has elasticity to allow an elasticsupport of the ball screw nut 412. The above table 6 has a suction plate418 on its top surface.

The above roller bearings 404 is composed of a retainer 406 formed intoa V shape and two or more rollers 408 which are secured onto each faceof the retainer 406 in such a way that they are allowed to rotatefreely.

Furthermore, roller bearing stops 430 which are provided atpredetermined positions near the limits of the movement of rollerbearings 404 associated with the low speed travel of the table 6 andwhich engage the retainer 406 to block forcibly the movement of rollerbearings 404, are provided, along with a shock absorber 432 which softlypushes the roller bearing stops 430, as is shown in detail in FIG. 16.

Therefore, since the ball screw 416 and the ball screw nut 412 areengaged, the table 6 can be moved at a predetermined speed by turning onthe driving motor 18 after setting the vertical position of the die 40,with the substrate A to be coated retained by the suction plate 418. Inthis case, as roller bearings 404 stand between the sliding stem 8 andthe V-shaped groove 402, the smooth and high speed movement of the table6 can be achieved. While the table 6 would normally develop a fairlylarge fluctuation in vertical position due to pitching and yawing as aresult of fluctuations in the diameters of the rollers 408 whichconstitue the roller bearings 404, this can be limited to within ±1 μmor sub-micron range, since each roller 408 performs only a rotatingmotion, unlike a linear motion guide which rotates and revolvessimultaneously.

Consequently, the fluctuation in the gap between the top face of thesuction plate 418 and the die 40 can be limited to within ±1 μm orsub-micron range.

Therefore, a coating with only a small fluctuation in thickness can beproduced on the substrate A by starting the discharge of a coatingcompound via the die 40 when the edge of the substrate A comes rightbelow the die 40.

In particular, when producing a thin-film coating using a low viscositycoating compound, e.g. using a Newtonian liquid of 30-50 centipoise inviscosity as a color filter coating liquid, the gap between the die 40and the glass substrate must inevitability be small, for example 100 μmor less, more preferably 50 μm or less. As a result, it is alsonecessary to improve the dispersion in the gap, for example to ±3 μm orless. While linear sliders based on conventional linear motion guidescannot cope with such strict demands, those using a linear sliderdescribed in this embodiment certainly can.

When coating on glass sheet substrates using a die coater of thisembodiment, it is necessary to increase the traveling speed of the table6 so as to increase productivity. In this respect, too, this embodimentis superior in that it can achieve considerably high traveling speeds(e.g. 10 m/min or more), significantly greater than 1-2 m/min which ispossible with a linear motion guide featuring high traveling accuracysliding bearings. Its accuracy is also excellent, with a high travelingaccuracy, not possible at all with a linear motion guide, and aresulting high coating accuracy achieved.

Moreover, when coating on glass sheet substrates, it is more common toset the backward traveling speed of the glass substrates higher duringtheir return travel than their forward traveling speed during theapplication of a coating liquid. This gives rise to slipping of rollerbearings 404 and their shifting to one end due to a great difference intraveling speed between the forward and backward travel. However, sincethe shifting of the roller bearings 404 are blocked by roller bearingstops 430, the function of the roller bearings 404 can be maintained,ensuring the long stable and smooth bi-directional movement of the table6.

In place of or in addition to the configuration shown in FIG. 16, tablelifting cylinders 434 designed to raise the table 6 after apredetermined number of two-way travels of the table 6 (which correspondto a number of shifting in the position of roller bearings 404 to themovement limit point or its vicinity) and roller bearing repositioningcylinders 438 designed to return the roller bearings 404 to apredetermined position in response to the lifting of the table 6 by thetable lifting cylinders 434, as shown in FIGS. 17 and 18, may beintroduced to deal with the problem of roller bearings 404 shifting toone end due to slipping.

The procedure to return the roller bearings is as shown in the flowchartin FIG. 19. Namely, the table 6 is moved to the end point of the forwardtravel, where the table lifting cylinders 434 and roller bearingreturning cylinders 438 are provided, and stopped. Then the table 6 islifted by the table lifting cylinders 434, and, with the load on theroller bearings thus removed, the roller bearing repositioning cylinders438 are extended to push back the roller bearings. Finally, thecylinders 438 and 434 are retracted one by one and the table 6 is placedon the roller bearings 404.

In this regard, the length over which the roller bearings 404 are pushedback is preferably equal to the length required to return the rollerbearing 404 to the original position. The number of two-way travels ofthe table 6 can easily be informed by the sheet substrate coatingcontrol unit (not shown in the drawing), as it is the same as the numberof executions of the sheet coating process. Moreover, the part 436 is anengagement member which engages the retainer 406 and is driven by thecylinder 438.

To push back the roller bearings 404 by means of cylinders 438, thetable 6 may be raised slightly (e.g. 0.1-1.0 mm) by a cylinder 434. Whenraising the table 6, the elastic deformation of the coupler 414 canprevent the ball screw 416, ball screw nut 412 and ball screw bearingsfrom being subjected to unnecessarily large forces, which preventsdegradation in the accuracy of the ball screw mechanism.

Similar effects can be achieved, if a rectangular groove is adoptedinstead of a V-shaped groove 402, along with rectangular stems 8 androller bearings 404 featuring flat retainers 406, although up and downmovement and yawing increase. Similar effects can also be achieved byinserting an elastic plate made of a substrate such as rubber at thejoint with table 6, in place of the coupler 414.

The quality of coated products depends not only on the means of coatingbut also on the comprehensive manufacturing method including the meansof coating.

An embodiment of the manufacturing method according to the presentinvention is shown in FIG. 20.

The apparatus used in this embodiment has a die coating unit 300 where acoating is applied on a substrate by a die 40, a substrate transfer unit302 which transfers the coated substrate 380 to the next process aftercoating, and a vacuum drying unit 330 which dries the coated substratein a vacuum. The substrate transfer unit 302 which is basically anunloader is made up of a cylindrical coordinates robot having anextendible arm 306 which is capable of up-and-down and turning motion.At the end of the extendible arm 306, two or more suction pads 304 isprovided which are capable of retaining a substrate via suction.

After coating is completed in the die coating unit 300, the suctionforce on the coated substrate 380 is released, and the substrate 380 onwhich a coating D has been formed is lifted from the table 6, as thelift pins extend from the surface of the table 6.

Then, as soon as the substrate transfer unit 302 operates to allow thesubstrate 380 to be secured on the suction pad 304 on the arm of theunit by suction, the arm 306 rises, removing the substrate 380 from thelift pins of the table 6 to pass the substrate 380 on to the vacuumdrying unit 330. In the vacuum drying unit 330, a shutter 332a is openedand the substrate transfer unit 302 operates to load the substrate 380onto the proximity pins 335 on the hot plate 333. The shutter 332a isthen closed, and vacuum drying is carried out by drawing out air fromthe interior via a vacuum pump 334. Heat is also applied to thesubstrate 380 by means of the hot plate 333. After vacuum drying iscompleted, a shutter 332b is opened, and the substrate 380 is passed onto a heat curing unit, not shown in the drawing, by a substratetransferring machine (not shown in the drawing). In the heat curingunit, the coating liquid is cured, by heating the substrate on the hotplate and keeping a predetermined temperature for a predetermined lengthof time, and by cooling it down on a cold plate. Heating on the hotplate is performed with the substrate 380 supported on pins.

Vacuum drying conditions include the degree of vacuum, which ispreferably 20 Torr or less in absolute pressure, more preferably 5 Torror less, still more preferably 2 Torr or less. If undertaken at apressure greater than 20 Torr, vacuum drying will take a long time. Ifit is to be performed larger than 20 Torr and there are requirements toshorten the drying time to increase productivity, such requirements haveto be met by raising the temperature, thereby increasing the evaporationrate. However, as the temperature increases, a viscosity of the coatingliquid decreases, making the coating liquid more susceptible todisturbances. As a result, it becomes difficult to prevent defects frombeing caused during the vacuum drying operation. To avoid bumps of thecoating liquid, the time required for the chamber interior gas pressureto reach the vicinity of the equilibrium vapor pressure of the solventunder a certain temperature condition, t1, is set within the bounds of 1sec<t1<120 sec in the operation of the vacuum dryer. Further, the timerequired to reach about 1 Torr is preferably set to about 60 sec orless, as this will help achieve swift and uniform vacuum drying.

The temperature is preferably 30° C. or greater and 180° C. or less,more preferably 40° C. or greater and 150° C. or less, still morepreferably 50° C. or greater and 120° C. or less. If undertaken at atemperature less than 30° C., vacuum drying will take a long time, andat greater than 180° C., an uneven temperature distribution occurs evenin vacuum drying, giving rise to vulnerability to the generation ofdefects. In addition, a temperature more than 180° C. can cause a largedecrease in viscosity of the coating liquid, making the coating liquidmore fluid and susceptible to the generation of defects such asproximity pin marks.

With the die coating unit 300, a coating can be produced within adesired rectangular coating area on a substrate A, with excellentpositioning and thickness accuracy. This is not possible with methodusing a spin coater, roll coater, etc.

When productivity is to be increased by drying and heat curing a coatingflawlessly formed on a substrate over a short period of time by using anordinary hot plate type oven, it is necessary to increase theevaporation rate by raising the temperature. However, when thetemperature is increased, the viscosity of the coating liquid decreases,making it more fluid and susceptible to disturbances. Moreover, sincethe evaporation rate is great, the rate of suction from the oven must beincreased to remove the vapors generated. The rate of airflow byconvection then increases, and this disturbs the surface of the coatingwhich has already become susceptible to turbulence, thus degrading thequality of the coating. In extreme cases, the coating liquid appliedwithin a rectangular coating area on the substrate can start migratingfrom the edge of the original coated area due to violent convection andan increase of its own liquidity, resulting in an extreme degradation inthe coating position and thickness accuracy.

With the above embodiment according to this invention, drying takesplace in a vacuum, so that even much lower temperatures will suffice toget as the same evaporation rate as in normal pressure. Therefore, thefall in viscosity and the increase in liquidity, of the coating liquidwill be small, so that disturbances in the coating surface due to theevaporation pattern, temperature fluctuations, convection, etc., can beprevented.

Namely, this embodiment of the coating method, involving coating using adie 40 and drying by vacuum dryer, can produce excellent products interms of coating area and quality which is not possible with other typesof coaters.

If a substrate positioning process as shown in FIG. 6 etc. is added tothe configuration shown in FIG. 20, the positioning and thicknessaccuracy of the coating applied on the substrate improves further.

In this example, there is only one vacuum drying unit, but there can bemore.

Usually, vacuum drying takes more time than coating, so thatproductivity can be improved by sending coated substrates to a number ofvacuum drying units one by one as they are produced, and passing them onto the next process after the completion of drying, as this will ensurethat the coating cycle time is not subjected to the vacuum drying time.

Moreover, in the vacuum drying unit 330, the suction outlet leading tothe vacuum pump 334 is preferably placed at a position which is higherthan that of the coated substrate 380 and does not directly face thecoated surface of the substrate 380. This is particularly true whenproviding a suction outlet in the top plate 336. More than one suctionoutlets are preferably provided in a distributed manner to obtain auniform dried film.

Usually, the chamber of the vacuum drying unit 330 is designed to have asmall capacity in order to maintain a uniform temperature distribution,and the distance between the coated substrate 380 and the top plate issmall.

Therefore, if a suction outlet is provided right above the coatedsurface of the substrate 380, temperature only in that part will differfrom that in other parts of the chamber, and as a result, evaporationcharacteristics there will differ from those in other parts, whichcauses changes in the coating characteristics in the portioncorresponding to the position of the suction outlet, making itimpossible to obtain products with uniform quality. In extreme cases,the suction outlet leaves its shape on the coating surface.

If the suction outlet is provided in the top plate 336, but in aposition not directly facing the coating surface, such defects can beprevented as variation in temperature distribution will not be caused inthe coating surface.

If the suction outlet is placed in a position which is lower than thatof the coated substrate 380, rising vapors will be pulled back andviolent convection will become likely to take place between the coatedsurface 380 and the top plate 336, thereby producing surface defects dueto disturbances on the coating surface.

EXAMPLES Example 1

Coating was carried out by: using a coating liquid for a green-pigmentedcoating, with a solid content by weight of 8 wt % and a viscosity of 25centipoise, prepared by mixing and dispersing chlorinated and brominatedPhthalocyanine Green (C.I. Pigment Green 36) with polyamic acid, apolyimide precursor, as binder in N-methyl-2-pyrrolidone as solvent;using a non-alkali-content glass substrate OA-2 (Nippon Electric GlassCo., Ltd.), measuring 360 mm×465 mm×1.1 mm, as a substrate A to becoated; and setting a slot gap LP and a clearance LC to 100 μm and 75μm, respectively. A syringe pump was used as a constant volume dischargeable pump. A high precision stepping motor was used to drive a table 6carrying a substrate, in conjunction with a sequencer for control. Acoating liquid tank 50 was charged with the coating liquid for apigmented coating, and a coating liquid path right up to a die 40 wasfilled with the coating liquid beforehand. To prevent the formation of acoating in marginal areas of the glass substrate up to 2 mm from bothedges, the length of the discharge outlet at the end of the slot inwidthwise direction was set to 356 mm.

After the substrate A to be coated had been fixed on the table 6 bymeans of vacuum suction, the substrate A to be coated was carried to aposition right under the die 40 by moving the table 6, and stoppedthere. At that time, the arrival of the table 6 to the position rightunder the die 40 was detected by a proximity sensor, and, after the die40 had been lowered to a position to obtain the predetermined clearanceas described above, the discharge of the coating liquid was started at arate of 285 μl/sec by activating the syringe pump 44. Then, after adesired coating liquid bead was formed between the die 40 and thesubstrate A throughout the width of the slot by maintaing the substrateat rest for just 0.5 sec, coating starts by driving the table 6 againwhich allows to move the substrate A relatively to the die, with amoving speed of the table 6 set to 3 m/sec. Almost immediately, theamount of coating liquid consumed in coating production equals to thatsupplied from the discharge outlet 66 of the die 40, establishing asteady-state coating condition in which a stable and continuous coatingwas produced. Similarly, proximity sensors were used to stop theoperation of the syringe pump 44 and the table 6 at the end-of-coatingline, while, at the same time, the coating liquid bead C formed betweenthe substrate A and die 40 was removed by sucking back 140 μl of coatingliquid via the discharge outlet 66 of the die by the reverse operationof the syringe pump 44. The die 40 was then raised away from thesubstrate A, and this completed the coating operation. The beginning andend of the coating line were set to be 1 mm from the lengthwise edges ofthe substrate. After this, the table 6 was reactivated to move thesubstrate to a loading position.

The coated substrate was then dried in a drying oven (not shown in thedrawing) for 20 min at 120° C. to obtain a green-pigmented coating. Thethickness profile of the coating produced is as shown in FIG. 21, and asteady-state coating thickness was obtained except up to 9 mm from thestart-of-coating line and 9 mm before the end-of-coating line. At boththe beginning and the end of the coating area, the coating thickness waswithin the range from 88% to 108% compared with that in the steady-statethickness area. FIG. 22 is a plan view of a glass substrate beingcoated, where hatching indicates the coating formed. The coatingproduced in this embodiment was of good quality throughout the intendedcoating area, from the beginning to the end of the coating area, withoutdiscontinuity or peeling.

Comparative Example 1

Coatings were produced on substrates in the same manner as Example 1except for the use of a gear pump instead of a syringe pump and theomission altogether of vertical movement of the die after the clearancewas set to 75 μm, the operation for stopping the table on its forwarddirection travel to the glass substrate unloading position, squeegeecoating, and the recovery of the coating liquid from the coating liquidbead by suction.

A typical thickness profile of coatings obtained from ComparativeExample 1 is as shown in FIG. 23, and a steady-state coating thicknesswas obtained in the intended coating area except for the sections within180 mm behind the start-of-coating line and 40 mm before theend-of-coating line. Near the end of the coating area, there was asection where thickness measurements were more than 300% of those in thesteady-state thickness section. The state of a coating formed on a glasssubstrate in this comparative example as viewed from above is shown inFIG. 24, where the coated area is shown with hatching, and the coatingwas not formed over the width direction within 22 mm behind thestart-of-coating line, leaving an uncoated portion.

Comparative Example 2

In this comparative example, coatings were produced on a substrate inthe same manner as Example 1 except that instantaneous positive pulseswere generated in discharging the coating liquid almost at the same timewhen the substrate passed right under the die, where positive means adirection to which coating liquid was discharged, instead of theomission of stopping the table at the start-of-coating line on itsforward direction travel, and that negative pulses were generated indischarging the coating liquid instead of the omission of the squeegeecoating at the end-of-coating line, as shown in the time chart in FIG.25.

A typical thickness profile of coatings obtained is as shown in FIG. 26,and a steady-state coating thickness was obtained in the intendedcoating area except for the sections within 28 mm behind thestart-of-coating line and 20 mm before the end-of-coating line. Due toinstability in the formation of the coating liquid bead, a temporaryfall in the coating thickness was observed near the start-of-coatingline. This tendency remained even when a rate of the coating liquiddischarge or a table traveling speed was changed. The state of thecoating produced on the glass substrate in this comparative example asviewed from above is shown in FIG. 27, where the coated area is shownwith hatching. According to this drawing, the generation of positivepulses in discharging the coating liquid alone could not form a uniformcoating liquid bead throughout the width of the substrate, and thecoating was not formed widthwise up to 8 mm behind the start-of-coatingline, leaving an uncoated section. Although an increase in the magnitudeof the pulses at the beginning of coating made it possible to produce acoating throughout the width right from the start-of-coating line, theresulting discharge of an excessive amount of the coating liquidincreased the coating thickness near the start-of-coating line, to aboutthree times the predetermined thickness.

Compared with Comparative Examples 1 and 2, Example 1 can provide alarger steady-state coating area, with the coating formed with aremarkably small margin near the edge of the substrate. With Example 1,furthermore, variations in coating thickness near the beginning and theend of the coating area were also greatly reduced, which is highlyadvantageous in a case where an advanced coating processing such aspatterning is to be performed in a subsequent step.

Example 2

A coating liquid for blue-pigmented coating, with a solid content byweight of 7 wt % and a viscosity of 20 centipoise, was prepared bydispersing Phthalocyanine Blue (C.I. Pigment Blue 15:4), to whichDioxazine Violet (C.I. Pigment Violet 23) has been added with a polyamicacid, a polyimide precursor, as binder in N-methyl-2-pyrrolidone assolvent. Similarly, a coating liquid for green-pigmented coating, with asolid content by weight of 8 wt % and a viscosity of 25 centipoise, wasprepared by mixing and dispersing chlorinated and brominatedPhthalocyanine Green (C.I. Pigment Green 36) in N-methyl-2-pyrrolidoneas the solvent. Furthermore, a coating liquid for red-pigmented coating,with a solid content of 5 wt % and a viscosity of 120 centipoise, wasprepared by mixing Dianthraquinonyl Red (C.I. Pigment Red 177). Anon-alkali glass substrate (OA-2), measuring 465 mm×360 mm×1.1 mmcovered with patterned chromium as a photo-shielding layer was retainedon the table 6 by means of suction. Simultaneously with theseoperations, the electromagnetic changeover valve 46 was switched over tothe coating liquid tank 50, and the syringe pump 44 was activated forsuction and was filled with the coating liquid. The filled volume was5,170 μl for the coating liquid for the red-pigmented coating, and 3,100μl for each of the coating liquid for the green-pigmented coating andthe coating liquid for the blue-pigmented coating respectively. Theelectromagnetic changeover valve 46 was then switched over to thecoating die to stand by for coating. At the same time, the die 40 waslowered to a position necessary to secure a 75 μm clearance. Then, thetable 6 was driven to move the glass substrate to a position right underthe die 40 and stopped. The arrival of the table 6 to the position rightunder the die 40 was detected with a number of steps generated by anencoder provided near the AC servomotor which drove the table 6, andthen the syringe pump 44 was activated to start the discharge of thecoating liquids of at a discharging rate of 518 μl/sec for the coatingliquid for red-pigmented coating, 308 μl/sec for each of the coatingliquid for green-pigmented coating and the coating liquid for theblue-pigmented coating respectively. After the substrate was maintainedheld at rest for 0.4 sec for the coating liquid for red-pigmentedcoating and 0.3 sec for the coating liquid for each of thegreen-pigmented coating and the coating liquid for blue-pigmentedcoating respectively from the beginning the discharge of the coatingliquid, the table was moved again at 3 m/min to start the coatingoperation.

When the arrival of the table at a point 5 mm before the end-of-coatingline was detected by counting the number of steps of encorder for the ACservomotor which drives the table, the syringe pump 44 was stopped,while the table 6 continued traveling. The rest of the coating area fromthis position to the end-of-coating line was coated with the so-calledsqueegee coating method in which coating is undertaken by consuming thecoating liquid bead C formed between the glass substrate and die 40.

When the substrate reached the end-of-coating line, the syringe pump 44was operated in the opposite direction, to withdraw by suction 90 μl ofthe coating liquid bead C through the discharge outlet 66 of the die ata rate of 360 μl/sec. Even during this operation, the table continued totravel at 3 m/min towards the unloader substrate transfer position.

After that, the die 40 was raised away from the glass substrate to endthe coating operation. The syringe pump 44 was then activated in theforward direction, to fill the die with 90 μl of coating liquid. Thecoated substrate was then dried at 120° C. for 20 min in a drying oven,and a positive resist was applied on the coating using the spinnermethod. Patterning by the so-called photolithographic techniqueinvolving masked exposure, development and etching was then carried out,followed by heating so as to perform an imidation reaction thereby tocreate red pixels. This process was repeated for the blue and greencoatings in turn under appropriate conditions to obtain pixels of red,green and blue, the three primary colors of light. A polyimide layer of0.9 μm thick was formed as a protective layer on the glass substrate onwhich pixels had been developed, and an indium-tin oxide film of 0.1 μmthick was further provided on this layer by sputtering to form atransparent conductive layer, resulting in a color filter. Four colorfilters measuring 10.4 in. diagonally were produced on this one glasssubstrate. For assessment purposes, pixel layer thicknesses of the samecolor was measured for each color after forming a pattern of each color.Pixels for each color were free of significant variations in coatingthickness, and the color filters produced exhibited excellentcharacteristics.

Example 3

After a coating liquid for red-pigmented coating was applied in the samemanner as Example 2, vacuum solvent removal was carried out by holdingthe coated substrate at 70° C. and 2 Torr for 3 minutes, followed bydrying on a hot plate (not shown in the drawing) at 130° C. for 10minutes. A positive photoresist (26.7 wt %, 20 centipoise) was thenapplied over the coated surface and dried to obtain a photoresist layer1.6 μm thick, in the same manner as the process for the coating liquidfor the red-pigmented coating except for that the filled volume was1,100 μl, the discharging coating liquid rate was 109 μl/sec and thetime for maintaining the substrate at rest at the beginning of coatingwas 0.8 sec.

Red pixels were then produced through patterning performed using theso-called photolithographic technique involving masked exposure,development and etching, and heating to perform an imidation reaction.The red pixel width was in a range of 90 μm (design value) ±1 μm, whichwas very precise, and there was no fluctuation of the width due tovariations in the thickness of the photoresist layer. By repeating thisprocess for the blue and green coatings in turn under appropriateconditions, pixels of three primary color, i.e. red, green and blue,were obtained. A die was used which measured 0.5 mm and 3.5 mm in thelengths of the bottom surfaces of the front lip and rear lip, L_(F) andL_(R), respectively, 100 μm in the width of the slot exit aperture,L_(P), 360 mm in the length of the slot exit aperture, W (i.e. a lengthin the lengthwise direction of the die), in the direction perpendicularto the coating direction.

A volume of the coating liquid, V, to be discharged to form a coatingliquid bead while the table was maintained at rest at the beginning ofcoating was set at 104 μl, 92 μl, 92 μl for red, green and blue,respectively, to satisfy the condition that it is equal to or greaterthan [L_(P) ×L_(C) ×W] and equal to or smaller than [(L_(F) +L_(R)+L_(P))×L_(C) ×W].

A polyimide layer 0.9 μm thick was formed as a protective layer on theglass substrate on which pixels had been provided by the aboveopearation, and a indium-tin oxide film 0.18 μm thick was further formedon this layer by sputtering to form a transparent conductive layer,resulting in color filters. Four color filters measuring 10.4 in.diagonally were produced on this one glass substrate. For assessmentpurposes, pixel layer thicknesses of the same color were measured foreach color after forming a pattern of each color. Pixels for each colorwere uniform in coating thickness, and the color filters producedexhibited excellent characteristics.

Example 4

A coating liquid for green-pigmented coating was applied on a glasssubstrate to produce a coating in the same manner as Example 1. Thesubstrate was transfered onto the four proximity pins in the vacuumdryer by an unloader, which is provided by a cylindrical coordinatesrobot as shown in FIG. 20. The substrate and the hot plate which heatsit faced each other, and were spaced apart by 3 mm, the distancecorresponding to the length of the proximity pins. Vacuum drying wasstarted by activating the vacuum pump as soon as the substrate had beentransferred. The vacuum drying conditions were a pressure of 1 Torr, ahot plate temperature of 50° C. and a drying duration of 3 min. The timetaken to reach about 1 Torr was about 30 sec. After drying, the driedsubstrate was transferred by another unloader to a hot-plate type heatcuring apparatus. The coated and dried substrate was heated for a minuteon the proximity pins (5 mm long) on the hot plate heated at 180° C.,held for 3 minutes on the proximity pins (5 mm long) on the hot plateheated at 130° C., and cooled down on a cold plate to cure the driedcoating.

The coating thickness after heat curing was 1.1 μm. The sample wasinspected for any coating irregularity using a backlight for a liquidcrystal display, and it was clear that the coating produced was freefrom defects such as pin marks due to uneven drying or temperaturedistribution, marks formed by the substrate transfer arm and marksformed by notches in the hot plates to facilitate for transferring.

Comparative Example 3

Coating, drying and heat curing were carried out in the same manner asExample 4 except for the omission of vacuum drying in a vacuum dryer,and holding for four minutes the coated substrate on the proximity pins(5 mm long) on the hot plate heated at 130° C.

Coating defects such as pin marks due to uneven temperaturedistribution, marks formed by the substrate transfer arm and marksformed notches in the hot plates to facilitate transferring, and soundcoating liquid application and curing could not be achieved.

INDUSTRIAL APPLICABILITY

The present invention makes it possible to stably produce coatedproducts with a high accuracy in coating position and coating thickness,without sacrificing the advantages of die coaters, such as economy, highaccuracy thin-film coating performance and an enclosed coating liquidenvironment. It is particularly suitable for coating sheet substratesand can therefore be applied to manufacturing coated sheet products suchas color filters for liquid crystal displays and solid-state televisioncamera tubes, optical filters, printed circuit boards, integratedcircuits and other semiconductor devices. It can present coated sheetproducts with an exceptional quality at low price.

What is claimed is:
 1. A coating apparatus which comprises a feedingmeans to feed a coating liquid, a coating liquid applicator having adischarge slot extending in one direction to discharge the coatingliquid fed by the feeding means, and a conveying means to move at leasteither the coating liquid applicator or a substrate to be coated withthe coating liquid relative one to the other, and said apparatus furthercomprising:(a) a first control means which comprises,(a-1) a positiondetecting means to detect position of the coating liquid applicator orthe substrate either of which is moved by the conveying means and (a-2)a controller capable of stopping the coating liquid applicator or thesubstrate which is moved by the conveying means at a position that isdetected by the position detecting means, such that a start-of-coatingline of the substrate is registered by the position detecting means uponalignment of the start-of-coating line with the slot of the coatingliquid applicator, and which controller is capable of starting movementof either the coating liquid applicator or the substrate that is stoppedat said position and maintaining the clearance between the exit apertureof the slot of the coating liquid applicator and the substrate at thestart-of-coating line; and (b) a second control means which comprises atimer controller capable of transmitting a signal to the controller ofthe first control means for movement of the coating liquid applicator orthe substrate which is stopped at said position, after a predeterminedperiod which begins with commencement of feeding the coating liquid andis needed for forming a coating liquid bead which is in contact withboth the exit aperture of the slot of the coating liquid applicator andthe substrate at the start-of-coating line and by the second controlmeans said predetermined period and the volume of the coating liquidbead formed at the start-of-coating line are controlled to regulate aprofile of the thickness of the coating liquid coated at the startingportion of coating on the substrate.
 2. A coating apparatus according toclaim 1, wherein the coating liquid applicator has at least a front lipand a rear lip, which are arranged together in the direction of therelative movement of the substrate with the front lip being first withrespect to the direction of the relative movement and wherein saidvolume V in mm³ of the coating liquid dispensed from the slot of thecoating liquid applicator after stopping the substrate to form thecoating liquid bead satisfies the following formula:

    L.sub.P ×L.sub.C ×W≦V≦(L.sub.F +L.sub.P +L.sub.R)×L.sub.C ×W,

where LF in mm is a length of the bottom surface of the front lip whichsurface is parallel to the direction of the movement, LR in mm is alength of the bottom surface of the rear lip which surface is parallelto the direction of the relative movement, LP in mm is a width acrossthe exit aperture of the slot, LC in mm is said clearance between theexit aperture of the slot and the substrate at the start-of-coatingline, and W in mm is a length of the exit aperture of the slot in thedirection perpendicular to the direction of the relative movement.
 3. Acoating apparatus according to claim 2, further comprising the featurethat the length of the bottom surface of the rear lip is longer thanthat of the bottom surface of the front lip in the direction of therelative movement.
 4. A coating apparatus according to claim 3, furthercomprising the feature that the length of the bottom surface of thefront lip is 0.01-0.5 mm measured in the direction of the relativemovement, while the length of the bottom surface of the rear lip is 1-4mm measured in the direction of the relative movement.